okay so finally we get to capillary pressure right we talked about pressure in the arteries this double up diastolic hypertension hypotension we talked about pressure in the veins how it's pretty low but we have ways to kind of help the blood get back to the heart because the pressure is so low now we'll talk about the capillaries just to get our kind of bearings remember pressure in the capillaries is relatively low right where is pressure the highest or what nozzles what kind of arteries the elastic arteries right the ones right by the heart pressures highest in the elastic arteries that are right by the heart and then as we go through the system what happens to the pressure it decreases right does it decrease all the way around the system or does it decrease down in the capillaries and then increase again decreases all the way through the system right pressures highest in the elastic arteries when we leave the heart and then it goes down down down down down down down the entire way through the system and its lowest in the vena cava right before we get back to the heart so the capillary to rate the middle victor we've lost a lot of pressure we've lost about 65 millimeters of mercury and pressure by time we get down to the paddlers the pressure is relatively low the cross-sectional area is very high right capillaries have the smallest diameter they're very very tiny but because we have so many of them the total cross-sectional area is high that means that there's a lot of resistance right that vessels are itty bitty little vessels and remember the smaller the vessel the more resistance to flow because all the blood is in contact with the vessel wall right where there's friction so that's why the blood flows so incredibly slowly through our capillaries I think is there's so much resistance with all of this cross-sectional area now remember that's great that's useful because what happens in the cap exchange okay nothing enters or leaves the bloodstream unless it's in the capillary so essentially we rush the blood to the capillaries and then we slow it down all right we have time for stuff to enter into the bloodstream and then we start just a few to back up then we brush it back to the heart now this capillary exchange that we're talking about is extremely important right nothing works without it like this essentially is life we get things out of the blood and deliver them to ourselves we take wastes and products away from ourselves this is life on what we talk about capital in exchange we move materials in and out of the blood across the capillary walls so thank you right and the capillary has how many layers in the capillary wall one right what layer is that either way their name would work right it's gonna pick intima which is the endothelium right at the endothelial layer so what kind of cells lot of these alignment simple squamous cells we call them endothelial cells so that's it then we have like a really thin basement membrane that's all we have we don't have muscle and a bunch of collagen like this is a really really thin walled vessel so we have these simple squamous cells one layer really really flat endothelial cells sometimes we see these little like junctions in between the cells and mites evil pores present in the south but it's a really thin wall that's the point and capillary exchanges talking about the exchange of materials between the blood inside the vessel and with the fluid called out here good the interstitial fluid that's out here right and then stuff goes to ourselves when we talk about how things move between the blood and the interstitial fluid there's multiple different forces that are involved and kind of pushing and moving materials back and forth we'll talk about diffusion which hopefully you guys are super familiar with we'll talk about filtration and also reabsorption last semester when I told you diffusion was like the most important concept you would learn so we'll start with diffusion which diffusion anything from high concentration to low concentration right if I put a drop of food coloring in a bunch of water the food coloring stop is thing in this one tight little drop where it's really concentrated the coloring is going to spread out right up by the end of the lecture we will have pink water you won't have clear water with one really red dot it will spread that's diffusion does this take energy no the cell doesn't have to spend any energy to make this happen right it's passive no AG P is required this is a passive process this nature causes this to happen again we'll talk about this more when we do respiratory but it's because the molecules are always moving right and a liquid and gas the atoms don't like stay still they're constantly bouncing all around so they spread out naturally that's diffusion now when we talk about things diffusing eating out of the bloodstream different molecules will take different routes to get in and out of the blood its diffusion so I'm always saying high concentration to low concentration but depending on what it is we're looking at it can go between smells it can go through a pore it can cross the cell I could just depend on what it is that we're actually looking at so water um ions so give me example of an ion calcium fluoride I charged molecules or if not molecules charged to atoms I guess these are ions so water ions and then small polar molecules like glucose they so small like glucose what do all of these things have in common water polar molecules like glucose ions they're all hydrophilic they're all charged in some way right either full charge like the ions or partial charge remember water is polar right there's the partial positive and partial negative all of these have some sort of charge because of that they're all hydrophilic where does hydrophilic leave water loving they like water because wipes dissolve like water is charged or it's polar right if their partial charges so things that have partial charges like it so they'll interact with each other just fine I use our hydrophilic now because of that remember when we look at these cells these endothelial cells were completely lined with the plasma membrane made of phospholipids right a phospholipid bilayer remember when we look at the plasma membranes we have two layers phospholipids in the middle is a bunch of lipids the lipids like water know right you put oil and water together and they separate you can shake it all you want where you set it down they're gonna separate they don't like each other so these things they're hydrophilic that like water do not like this liquid core in the plasma membrane ourselves so they do not want to travel directly across it they won't they do not want to come does with it so when they're crossing in and out of the bloodstream they need some other place to cross some other way to get in and out so they can do it a couple different ways they can go between and change their kind of the illegal cells we have small flex present between cells and our continuing in our normal and continuous capillaries and that would allow some of these really small hydrophilic things to cross in and out of the bloodstream we also have some channels present channels remember are like little tunnels names they're tiny little tunnel that will allow things to cross in and out of the cell without actually having to come in contact with that lipid bilayer so we do have some channels present that will allow these to go through like aquaporins our water pours but we do have some channels are like sodium channels passing channels those things allow things to cross and then also remember fenestrated capillaries have larger pores present that allow these things to cross really rapidly okay so remember we sent me zombies fenestrated capillaries in the intestines we're all still easy then kidney and then some of our endocrine glands because again in these areas it's important for this stuff to be able to to cross to get in and out of the blood really really fast making your intestines we're absorbing a lot of ions a lot of glucose a lot of stuff has to get absorbed to really rapidly into the blood so we like these quarters or fenestrations so we don't have to like slowly way for this process to occur for all of the tiny little channels happens really faster the force so but this is not the only stuff that has to diffuse in and out we have some larger water soluble compounds so these would be things like seven four mountains and they're like polypeptides what's a polypeptide multiple peptides right still like on the way to becoming a protein you put multiple amino acids together right now we can call that a polypeptide can give you amino acids it can be a lot of amino acids but you string together some of them you know acids we call that a polypeptide it's big right relativity big bigger than like glucose so these things are pretty big but they're still water soluble they like water so do they like this lipid bilayer no so they're not gonna go straight through the cells so they need some sort of hole these are there notice I said large they're too big for these itty bitty cleft in between the cells in our continuous capillaries so these cannot cross in our continuous capillaries we need fenestrated Cowboys because what if fenestrated capillaries have larger pores right take a larger passageways present so again I just told you about this but where do we see these intestines kidding me why I'm stuck hormones and no cream glands hey again places where we might need to absorb a lot of polypeptides or places where we might need to these secreting hormones under the blood scream um so lipids and lipid soluble materials so things like fatty acids okay but more importantly what two things can you tell me that our lipid soluble that we would have crossing in and out of the blood all the time and beautiful and oxygen and carbon dioxide their respiratory gases those are lipid soluble so anything that's the small bit soluble things can go directly through the end of the little cells a their lipid soluble they like lipids they don't mind this lipid bilayer so those things paint a few straight through the plasma membranes of the cells they don't need a cleft they don't need a gap they don't need a pore they very easily just cross straight through it cells to get in and out of the bloodstream now again that's one of the reasons why it's so important we have such a thin little barrier if we had a bunch of cells stacked on top of each other it would be a lot harder to go through just remember distance matters when we're talking about diffusion this is a nice short little distance with just fat Tunica intima finally we have really really big things halite plasma proteins or blood cells these things are too big to even fit through the pores and the fenestrated capillaries so remember we have highly specialized capillaries that are called sinusoids and we have those in areas like the liver good their livers clean the bone marrow okay so like where do we make plasma proteins good deliver okay so we have top sinusoidal liver so that once we make them we can push them into the blood easily so we've got bigger gaps present between cells and these sinusoids to fit the really big stuff through it so but again remember that this is diffusion so what does that mean I'm going from what to what kind a load so understand right after that diffusion is going from high concentration to low concentration depending on what the molecule is it's gonna take a different route to get in and out of the blood so be able to combine those concepts like if I say that I have more oxygen in the blood right or the concentration of oxygen is higher in the blood than in the interstitial fluid what's going to happen oxygens getting diffuse to the interstitial fluid how straight through right straight through the endothelial cells Hey or if I'm talking about plasma proteins that I have more plasma proteins in the interstitial fluid because say I'm in the liver and I just made them that otherwise what would not happen but I have more plasma proteins in the interstitial fluid where are they going to diffuse into the blood how through the gaps between cells and sinusoids some diffusion is one way that things get in and out of the bloodstream filtration is another force that allows us to push things out of the blood and kind of drive this capillary exchange or this mix between the blood and the interstitial fluid so in general penetration occurs when we remove solids as a solution is forced like pressure physically forced across the porous membrane if you give anytime you filter anything like in your water right to your water like if you have a filter on your water at home the liquid is forced to pressure across some Jordan filter or a membrane the liquid comes through some solutes make it through if they're small enough they come through the bigger solutes get trapped in the filter right that's exactly what filtration is in the blood we're pushing fluid forcefully pushing it from the blood into the interstitial fluid the wall of the vessel creates our filter right because it's a porous membrane there are pores that allow some things through but other stuff can't make it through the membrane other stuff gets trapped because it's too big so we're literally just filtering things from the blood across the vessel wall into the interstitial fluid when we see this happening we see in the vessels it's driven by a pressure called hydrostatic pressure again that's just physical force and think about it we have the heart generates all this pressure so this blood gets forced forward with pretty good pressure and we're creaming a bunch of fluid into tiny itty-bitty little vessels microscopic little puzzles so you could imagine the fluid has some pressure that's pushing out with right as the fluid gets pushed forward it's pushing in all the direction so it's pushing out on the vessel walls that's hydrostatic pressure the physical pressure pushing against the wall as the blood is crammed into that small vessel again it's can't push water and small solutes that can make it across the membrane from areas of high pressure to pressure so as long as the pressure in the vessels is more than the pressure in the interstitial fluid we'll have some pressure that fits driving filtration we see that water and small solutes so things like ions things like glucose get forced across the capillary wall into the interstitial fluid alright they're small enough to fit and they little collects between cells and they can get pushed out and into the interstitial fluid but larger solutes are stuck in the blood okay so what's a really big solute plasma proteins proteins cells basically if your red blood cells are too big to get pushed out from the blood in the interstitial fluid so we're pushing all of them the water and the small stuff out we're leaving the really big solutes in the blood and this could kind of vary depending on what type of capillary we're looking at guys but I'm just let's just think really generally like continuous catheter reabsorption hey just thinking really generally what is when you reabsorb something what do you do take it back right like filtration is when we push the fluid out when we reabsorb it absorb right we take it back in again so reabsorption is the opposite of filtration filtration is when we put out reabsorption is when we pull fluids and solutes back into the bloodstream reabsorption it's not the results of hydrostatic pressure it's not that physical force of the pressurized blood pushing out it's the result of osmotic pressure you guys remember osmosis in general with the simplest definition of osmosis beautiful the diffusion of water hey remember we want to even out osmotic pressure x' which is like the concentration of stuff right all of the solutes in the fluid that relates to its osmotic pressure its osmolarity and we want to have even or nature wants to have even concentrations of stuff inside and outside of the blood so with diffusion we're looking at each individual Sawyer right Jessica Lacoste just oxygen just sodium with osmosis we're looking at all of them put together all the solutes together combined with diffusion we say that that one solute that we're talking about goes from high concentration to low concentration right if I have more women in the blood it's going to diffuse out to the interstitial fluid but with those motions I'm saying that can't happen if I have more plasma proteins in the blood I can't have them diffuse out to the interstitial fluid they're stuck right they can't leave so I was stuck with all these solutes in the blood and I can't get him out so the only thing we can do to try to even up concentrations is to then increase the amount of fluid in the blood all right thank the concentration will decrease if you can't decrease the soil yes you can you increase the fluid so that's this this osmotic pressure or osmotic PO I think is it an easier way to understand is describing it as osmotic pull because it pulls fluid back into the blood stream and we call it the blood colloid osmotic pressure it's the osmotic pressure or us what it pull of the blood mostly because of all of the plasma proteins that are stuck in the blood stream that won't actually diffuse out or won't get filtered out technically as my pressure is the pressure the physical force that's required to prevent osmosis maybe that just like the dish sounds like too much the easiest way I need to think of it it's interesting that the higher the concentration of solutes osmotic pressure these are the more stuff you have the more the osmotic pressure is and the water is always gonna cross to the side with more stuff so there's always this interplay going on between filtration and ribs or connect they both of them are happening in the capillary event so we see that we push stuff out and then we pull stuff back in and it creates this kind of flushing action right and that ensures that the interstitial fluid in the plasma are always in communication with each other it's really important for preventing like little kind of clusters of really high ion concentrations or clusters of you know hormones are just the clusters of you we want to kind of keep everything filtering and moving and spread out throughout the body this is also important because it helps to accelerate nutrients the movement of nutrients whether we're absorbing them or whether we're distributing them into cells and we just rely on diffusion alone it wouldn't happen quick enough we wouldn't be able to drop things off quick enough by time the blood left the capillary bed so this filtration reabsorption is flushing action helps to speed up all of that so that we make sure we can deliver nutrients quick enough it's also important for the immune system well look at this in a little bit but we'll see how some of this fluid ends up making its way for the lymphatic system and that's what we run it through lymph nodes and we screen and we look for pathogens so that we can alert the immune system to an infection that might be present in the periphery so it's really important that we have this filtration reabsorption occurring